1. Field of the Invention
The present invention relates to a system and method for dissipating excess heat from integrated circuit semiconductors. More particularly, the present invention relates to a system and method for dissipating excess heat through the use of externally and internally located heat sinks for molded flip die (MFD) packaged integrated circuits.
2. Background Information
An integrated circuit (IC) package is a structure used to electrically connect an IC die (die) to a printed circuit board (PCB) or other host structure. Each die typically includes input/output (I/O) terminals which are arranged along a peripheral edge of the die. After the die is mounted on a package, the I/O terminals are electrically connected to bonding pads formed on the package using, for example, wire bond techniques.
In order to maintain a reasonable service life of an IC device, the operating temperature of the device must be carefully controlled by providing adequate heat dissipation. To keep pace with the developments in IC fabrication, there is an on-going need for IC packages having improved thermal characteristics. The term “thermal characteristics” is used herein to refer to a package's ability to dissipate a large amount of heat generated during operation of the die such that the die is maintained at an optimal operating temperature.
A conventional plastic semiconductor package includes a semiconductor die wire bonded to a lead frame, and encapsulated in a plastic body. One consideration in designing a plastic package is heat transfer from the die. In a conventional plastic semiconductor package, the bulk of heat transfer from the encapsulated die is through the terminal leads of the package. However, as circuit densities increase, semiconductor die generate additional heat, and the leads of the package are not always able to efficiently dissipate the heat.
The higher power consumption circuits in modern IC devices creates the need for improved heat dissipation. A heat sink normally made of a high thermal conductive material has been used to fulfill the need for improving heat dissipation in plastic molded packages. A heat sink is typically made of a material that has high thermal conductivity such as copper, copper alloys, aluminum, aluminum alloys or any other high thermal conductive materials. The heat sink ideally should be in good thermal contact to a semiconductor die.
FIG. 1 illustrates a cross sectional view of a conventional molded flip die (MFD) IC 2. Use of the solder balls 20 between the die 22 and the lead pads 6 provides the electrical path between external circuits, components (passive and resistive), I/O connectors, and other devices, and the internal circuitry of the die 22. Each solder ball 20 is in electrical communication with at least one internal connector, or terminal, of the die 22. Encapsulating the die 22, solder balls 20, and several sides of the lead pads 6 is an encapsulating or molding material 12. The molding material 12 can be a ceramic material, although an epoxy-resin based material (plastic) can be used that saves weight and reduces costs. Plastic, however, is not as good a thermal conductor as ceramic, and MFD ICs 2 (and other types as well) can be required to dissipate 5, 10 or even up to 20 watts of power.
Because of its small size, increasing numbers of MFD packages can be located on a PCB, increasing the amount of heat need to be dissipated by the PCB per given area. Thus, a need exists for an improved MFD package that can dissipate greater amounts of heat.